Our current view of the hemodynamic basis of atherogenesis can be summarized as follows: 1. Intimal thickening is a response of arteries to hemodynamic forces, occurring locally where the wall shear stress is sustained below a critical range (ca. 10-15 dynes/cm2). 2. Atherosclerotic plaque development requires the additional factor of long residence time of circulating atherogenic substances near specific sites of the artery wall. Project 0031 is designed to investigate these two viewpoints. Project 0031 builds upon our current SCOR research to examine the important question of whether the hemodynamic correlations between wall shear and intimal thickness observed in the human carotid artery also hold for the human coronary arteries. Significantly, the quantitative measurement of particle residence time is introduced for the first time, utilizing an experimental technique developed under current SCOR funding. Additionally, models of the human coronary arteries will serve as a test bed to examine the effects of heart rate and flow conditions upon particle motion. The results from Project 0031 will identify hemodynamic factors relevant to the studies of cultured endothelial cells in Project 0034 and to the design and interpretation of the in vivo investigations of Project 0032.